Tar sand separation process using solvent,hot water and correlated conditions



United States Patent 3,509,037 TAR SAND SEPARATION PROCESS USING SOLVENT, HOT WATER AND CORRE- LATED CONDITIONS Harold F. Tse, Bala Cynwyd, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jerse y Filed Aug. 11, 1967, Ser. No. 659,903

Int. Cl. Cg 1/00 U.S. Cl. 20811 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method for the processing of bituminous tar sands. The process comprises first forming a mixture of the sands and a solvent. The solvent is characterized by having a boiling range above the boiling point of water under the same conditions. The sands and solvent are then mixed with superheated water at correlated conditions of temperature and pressure such that substantially no vaporization of water occurs. The tar sands, solvent and superheated water are then discharged into a separation zone operated under correlated cond1- tions of temperature and pressure such that at least a portion of the water in the mixture is vaporized into bitumen froth forming steam to form an upper bitumen froth layer, a middlings layer comprising water, clay and bitumen and a sand tailings layer. This process allows the recovery of a higher amount of bitumen froth over that recovered in a conventional hot water process.

This invention relates to a method for the processing of tar sands. Large deposits of these sands are found as the Athabasca deposits in northern Alberta, Canada. The evaluated portion of these deposits occupies about five and one-half million acres and is buried by zero to 2000 feet of overburden. It has been estimated that these deposits consist of about 600 billion barrels of reserves in place, over 350 billion barrels of recoverable reserves of raw tar sand oil and over 250 billion barrels of upgraded synthetic crude oil. See page 1 of the K. A. Clark Volume edited by M. A. Carrigy, Research Council of Alberta, October 1963. The recoverable reserves estimate is just about equal to the world-wide reserves estimate of conventional oil, sixty percent of which is in the Middle East.

The tar sands are primarily composed of a fine quartz sand having a particle size greater than that passing a 325 mesh screen. The quartz sand is impregnated with a viscous bitumen in quantities of from 5 to 21 weight percent of the total composition. More typically the bitumen content is from 8 to percent. This bitumen is quite viscous6 to 8 API gravityand contains typically 4.5 percent sulfur and 38 percent aromatics. Its specific gravity at 60 F. ranges typically from about 1.00 to about 1.06.

In addition to the bitumen and quartz sand, the tar sands contain clay and silt in quantities of from 1 to 50 weight percent of the total composition. Silt is normally defined as material which will pass a 325 mesh screen but which is larger than 2 microns. Clay is material smaller than 2 microns including some siliceous material of that size.

Several basic extraction methods have been known for many years for the separation of bitumen from the sands. In the so-called cold water method, the separation is accomplished by mixing the sands with a solvent capable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water with a surface agent added, or a solution of a neutral salt in 3,509,037 Patented Apr. 28, 1970 water. The combined mass is then subjected to a pressure or gravity separation.

In the hot water method, the bituminous sands are jetted with steam and mulled with a minor amount of hot water at temperatures in the range of to 210 F. The resulting pulp is dropped into a stream of circulating hot water and carried to a separation cell maintained at a temperature of about to 200 F. In the separation cell, sand settles to the bottom as tailings and bitumen rises to the top in the form of an oil froth. An aqueous middlings layer containing some mineral and bitumen is formed between these layers. A scavenger step may be conducted on the middlings layer from the primary separation step to recover additional amounts of bitumen therefrom. This step usually comprises aerating the middlings as taught by K. A. Clark, The Hot Water Washing Method, Canadian Oil and Gas Industries, 3, 46 (1950). These froths can be combined, diluted with naphtha and centrifuged to remove more water and residual mineral. The naphtha is then distilled off and the bitumen is coked to a high quality crude suitable for further processing.

The present invention relates to an improved method for separating bitumen from tar sands. The invention can be described in one aspect as comprising first forming a mixture of bituminous tar sands and a solvent, said solvent characterized by having a boiling range above the boiling point of water under the same conditions. Usually this boiling range will be between 250 to 800 F. The tar sands and solvent are then mixed with superheated water at a temperature above the boiling point of water but at a pressure such that the water remains liquid. The tar sands, solvent and superheated water are then discharged into a separation zone operated at a temperature and pressure at which at least a portion of the superheated Water boils. Preferably the separation cell is operated at atmospheric pressure and at a temperature near 212 F. A preferred temperature range at atmospheric pressure is 180 to 210 F. At these conditions of temperature and pressure at least a portion of the superheated mixture in the feed to the cell boils, forming vapor bubbles which allow the recovery of a higher amount of bitumen froth over that recovered in a conventional hot water process. Thereafter the froth, middlings and sand tailings in the separation cell can be treated as in a conventional hot water process.

The conditions under which the water is initially mixed with sands and the conditions in the separation zone are correlated so that no boiling of either solvent or water takes place in the mixing stage and at least a portion of the water in the sand pulp boils in the separation stage while substantially no solvent boils. In the forming stage, these conditions will generally fall within a temperature range between 220 and 325 F. and a pressure range of between 16 and 100 p.s.i.g. More usually the temperature will be between 250 and 300 F. and the pressure between 30 and 70 p.s.i.g. The separation zone will most often be operated at atmospheric pressure and temperatures between about 180 to 210 F. The conditions in either stage can be widely varied substantially as long as they are correlated as described. For example, although it is preferred that the separation zone is operated at atmospheric pressure and at a temperature in the range of about 180 to 210 F., the zone can be operated at different temperatures at elevated or reduced pressures so long as these conditions are correlated with the c nditions in the mixing zone as described supra.

In this specification the term correlated means adjusted so as to give the recited result. For example, correlated conditions of temperature and pressure such that substantially no vaporization of water occurs means that for any given temperature, the pressure is adjusted, so that water 3 does not boil or for any given pressure the temperature is correspondingly adjusted. Thus conditions could be such that temperature would be above the boiling point of water at atmospheric pressure, i.e., 212 F. but that the pressure would be elevated to prevent substantial water vaporization.

The initial addition of solvent and water to the sands can be conducted in any desired sequence, however it is preferred to first add the solvent to the tar sands followed by addition of the water. The solvent performs the function of dissolving the bitumen thereby reducing its viscosity and making it more mobile and susceptible to the strip ping force of the aqueous phase. It can also reduce the specific gravity to a point below that of the water thus facilitating separation in the later stage. The water added more easily penetrates the bitumen to the sand particles thus promoting the separation of the bitumen from the sand.

The added water is superheated so that upon discharge into the atmospherically operated separation zone, at least a portion will vaporize to form additional froth. It might seem that because mineral and sand are more hydrophilic than bitumen that the water vapor bubbles in the separation cell would contain a high degree of these materials. However, the density of the mineral and sand is substantially more than that of the bitumen so that the bitumen and water vapor rise in the cell divorced from the solids. Furthermore, the violent bubbling caused by vaporizing water causes agitation which tends to shear any residual associated mineral from bitumen to promote an even higher recovery of froth.

Another advantage of the present process is that any vapor lost from the separation cell is water. In reducedpressure flotation processes which utilize vaporized solvent, any lost vapor is significantly more expensive than water. In some cases the lost vapor will create a health or combustion threat. The present process is advantageous over the known reduced-pressure flotation processes in this respect also.

The invention will be described in detail with reference to the drawing which shows schematically the process of the present invention.

Bituminous tar sands are fed into the system through line 1 where they pass into a first mixing zone 14 where they are thoroughly mixed with solvent from line 2. If desired the tar sands can be screened before mixing with solvent. The solvent can be any diluent which has the ability to dissolve the bitumen constituent of tar sand and to reduce its viscosity thereby. Additionally the solvent must have a boiling range above that of water under the same conditions of pressure. Usually the boiling range is between 250 to 800 F. Preferably the range is 300 to 500 F. Preferably the solvent has a density less than that of water under the same conditions. Petroleum fractions such as some naphtha, kerosene, gas oil distillates, furnace oils and aromatic hydrocarbons are suitable if their range or boiling point is above that of water. Suitable aromatics include the xylenes. The suitable non-hydrocarbon solvents include n-butanol and the C and heavier alcohols especially octyl and lauryl alcohol. Mixtures of solvents are also suitable. Generally the solvent is characterized by having aboiling range between 250 to :800" F. at atmospheric pressure. Preferably the solvent will have a boiling range between about 300 to 500 F.

The amount of solvent added will vary with the composition of the tar sands and the particular solvent employed. However generally it can be said that the proportion of solvent to weight of tar sand plus solvent may range from about 5 to 20' weight percent. In one embodiment of the present invention, the first mixing zone 14 is operated at an elevated temperature. In such an instance, the proportion of solvent may vary outside of this range. Preferably, at room temperatures, the solvent will be added in an amount ranging between about 7 and about 10 weight percent of the total of solvent and tar sands.

Although the drawing shows separate mixing zones 14 and 15 and successive addition of solvent and water, the present invention can utilize a single combined mixing zone and simultaneous addition of solvent and liquid.

After the solvent and tar sands are thoroughly mixed in zone 14 the mixture is discharged via line 3 to pressure mixing zone 15. This Zone is operated at a temperature above the boiling point of water but at such a pressure that no vaporization of water occurs in the zone. In this zone 15 the tar sands and solvent are mixed with superheated water from line 4 which may be superheated fresh water or a superheated middlings recycle stream from line 5. The total amount of water introduced from line 4 may vary considerably but should be sufficient to completely wet the sand particles in the tar sands. Usually the amount of water to total composition will be at least 50 weight percent. Preferably the amount of water added will be Within the range of 30 to 70 weight percent water to the total composition of tar sands, solvent and water.

The mixture or slurry of tar sands, solvent and superheated Water passes from the pressure mixing zone 15 through line 6 to the separation zone 16 containing water which is operated at atmospheric pressure and at a temperature near but not above the boiling point of water so that some superheated water entering zone 16 flashes to form vapor bubbles. In the separation zone 16 the slurry forms into bitumen and solvent froth which rises to the cell top and is withdrawn via line 7 and a sand tailings layer which settles to the bottom and is withdrawn through line 8. As described supra, vapor bubbles from the superheated water in the slurry provide increased bitumen froth. An aqueous middlings layer forms between the froth and tailings layers. A portion of this layer may be recycled through line 5, heated and added as a portion of the superheated water added to the pressure mixing zone 15. A portion of the middlings may be withdrawn from the separation zone 16 and sent through line 9 to a scavenger zone 17 wherein an air flotation operation is conducted to cause the formation of additional bitumen froth.

The processing conducted in the scavenger zone involves air flotation by any of the air flotation procedures conventioinally utilized in processing of ores. This involves providing a controlled zone of aeration in the flotation cell at a locus where agitation of the middlings is being eifected so that air becomes dispersed in the middlings in the form of small bubbles. The drawing illustrates a flotation cell of the sub-aeration type wherein a motorized rotary' agitator is provided and air is fed thereto in controlled amounts. Alternatively the air can be sucked in through the shaft of the rotor. The rotor effects dispersion of the air in the middlings. This air causes the formation of additional bitumen froth which passes from the scavenger zone 17 through line 10 to a froth settler zone 18. An oil-lean middlings stream is removed and discarded from the bottom of the scavenger zone 17 via line 11.

In the settler zone 18, the scavenger froth forms into a lower layer of settler tailings which is withdrawn and recycled via line 12 to be mixed with oil-rich middlings for feed to the scavenger zone 17 via line 9. In the settle zone an upper layer of upgraded bitumen froth forms above the tailings and is withdrawn through line 13 and mixed with primary froth from line 7 for further process.

In the process, an alkaline reagent can be added with water addition to the pulp to control the pH in the separator 16. The amount of reagent preferably is regulated to maintain the pH of the middlings layer within the range of 7.5 to 9.0. Best results are obtained at a pH value of 8.0 to 8.5. The amount of alkaline reagent that needs to be added to maintain a pH value in ranges of 7.5 to 9.0 may vary from time to time as the composition of the tar sands as obtained from the mine site varies. The best alkaline reagents to use for this purpose are caustic soda, sodium carbonate or sodium silicate although other reagents can be used.

The following example illustrates the process of the present invention. Specifically the example shows that low bitumen tar sands can be processed by the invention to give excellent yields of recovered bitumen.

On an hourly basis 1000 tons of screened bituminous tar sands with an average composition of about 8 weight percent bitumen, about 2 weight percent water and about 90 weight percent sand and clay are fed into a mixing vessel where they are agitated along with 60 tons of kerosene. The kerosene diluent has a boiling range of about 300 to 500 F. and a specific gravity of about 0.8. The resulting specific gravity of diluted bitumen in the tar sands is about 0.9. The agitation of tar sands with the kerosene solvent produces a pulp which is then passed to a pressure mixing zone operated at about 250 F. and at 30 p.s.i.g. pressure. The pulp is mixed with about 3000 tons of hot water and agitated to give a slurry of tar sands and diluent in hot superheated (250 F.) water. The slurry is then charged into a separation cell which is operated at atmospheric pressure. A portion of the superheated water in the slurry boils upon the discharge into the separation cell. A bitumen froth forms at the top of the water in the cell and a sand layer forms at the cell bottom. Sand tailings are removed from the cell at the rate of about 800 tons per hour and froth is recovered at the rate of about 130 tons per hour. The compositions of the tailings and froth are given in the table. The bitument content of the froth corresponds to a net recovery of over 80 percent of the bitumen in the original tar sands.

TABLE Tons per hour Tar sands feed 1000 Bitumen 80 Mineral 870 Water 50 Kerosene diluent 60 Water feed 3000 Separation cell tailings 800 Bitumen and kerosene 5 Mineral 600 Water 195 Primary froth 180 Bitumen and kerosene 130 Mineral Water 40 Middlings 3080 Bitumen and kerosene 5 Mineral 260 Water 2815 This example shows that excellent yields of bitumen froth can be obtained by the invention applied to tar sands of low bitumen content.

What is claimed is:

l. A process for separating bitumen from bituminous tar sands which comprises:

(a) formingva mixture of said sands, water and a solvent said solvent characterized by having a boiling range above that of water at atmospheric pressure, said forming step conducted at a temperature of between about 220 and 325 F. and a pressure of between about 16 and p.s.i.g., said forming step conducted so that substantially no vaporization of water occurs;

(b) passing the mixture to a separation zone operated under correlated conditions of temperature and pressure so that at least a portion of the water in said mixture vaporizes into steam to form an upper bitumen froth layer, a middlings layer comprising Water, clay and bitumen and a sand tailings layer; and

(c) separately removing from said separation zone said bitumen froth layer and said sand tailings layer.

2. The process of claim 1 in which said solvent is characterized by having a boiling range above about 250 to 800 -F. at atmosphere pressure.

3. The process of claim 1 in which said solvent is characterized by having a boiling range between about 300 to 500 F.

4. The process of claim 3 in which said separation zone is operated at a temperature of between about 180 to 210 F. at atmospheric pressure.

5. The process of claim 1 in which said separation zone is operated at a temperature of between about 180 to 210 F. at atmospheric pressure.

6. The process of claim 1 which additionally comprises passing at least a portion of said middlings layer to a scavenger zone and therein recovering an additional amount of bitumen froth.

7. The process of claim 1 in which said forming step is conducted at a temperature of between about 250 and 300 -F. and a pressure of between about 30 and 70 p.s.i.g. said temperature and pressure correlated so that said water does not substantially vaporize.

8. The process of claim 7 in which said separation zone is operated at a temperature of between about 180 to 210 F. at atmospheric pressure.

References Cited UNITED STATES PATENTS 3,041,267 6/1962 Frame et al 20811 3,208,930 9/1965 Andrassy 20811 3,401,110 9/1968 Floyd et a1 20811 3,422,000 1/ 1969 Bichard 20811 DELBERT E. GANTZ, Primary Examiner T. H. YOUNG, Assistant Examiner 

